(a) Field of the Invention
The present invention relates to a safety device for preventing overcharging of a battery, in particular, to a safety device which can prevent safety accidents attributable to overcharging of a battery by interrupting supply of electricity to a battery stack.
(b) Description of the Related Art
Recently, in order to prevent environmental pollution caused by use of fossil fuels, environmentally-friendly vehicles which run on electricity, such as a hybrid vehicle, are in greater demand.
An environmentally-friendly vehicle typically uses a battery which stores electric energy. The battery needs to have a high storage capacity so that the vehicle can run on electricity. Accordingly, medium or high capacity batteries are used for environmentally-friendly vehicles.
However, it is difficult to install a medium or high capacity battery in a vehicle because medium or high capacity batteries often are large and heavy. For this reason, miniaturization of the batteries is needed. Recently, a battery structure using a pouch which can meet such a demand has attracted attention. The battery structure using the pouch has high electric efficiency but low stability. For this reason, a technology which can ensure safety is needed.
When the battery using such a battery pack is overcharged, the battery undergoes overheating, a voltage rise, and swelling in which the battery is inflated due to gas generated. Accordingly, a high voltage battery system needs to be equipped with a safety device for prevention of overcharging. When overcharging occurs, a safety device for preventing overcharging intercepts a current in order to prevent thermal runaway, thereby preventing explosion of a battery system.
A passive-type safety device for preventing overcharging according to a conventional art uses an inflation pressure which is generated at the time of cell swelling. When the cell swelling sufficiently progresses, a cell inflates through an opening formed in an end plate, and finally a cell tap is fractured. Through this process, electric current is intercepted and safety is secured.
In order for this mechanism to operate, the cell swelling needs to sufficiently progress before thermal runaway occurs. When the cell swelling does not reach a sufficient level before the thermal runaway occurs, even though this mechanism starts operating at the same time as the occurrence of thermal runaway, explosion of a battery may occur due to thermal runaway. When the amount of gas generated is not sufficient, the cell tap may not be fractured.
As an alternative method of preventing overcharging of a battery, there is an active-type method which actively cuts off a relay.
The active-type safety structure for preventing overcharging is equipped with a sensor for detecting inflation of a cell or a switch, and intercepts current supplied to a battery system by interrupting supply of power to a relay when cell inflation is detected.
However, a technology which interrupts supply of power to the relay cannot block the flow of current when the relay is short-circuited. In an emergency such as an accident, the active-type overcharging-preventing safety structure is difficult to secure safety when electrical/electronic components are out of order, for example, when a sensor or a switch malfunctions.
In general, a passive-type overcharging-preventing safety structure is more reliable than an active-type overcharging-preventing safety structure, so there is a demand for improvement in technology of the passive-type system.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.